1. Technical Field
The inventive concept disclosed herein relates to signal processing, and more particularly, to a signal transmitting device adjusting an electrical characteristic value corresponding logic level and a signal transmitting method thereof.
2. Description of the Related Art
Recently, various wireless communications are provided based on an Orthogonal Frequency Division Multiplexing (OFDM) method. The OFDM method divides one data string into a plurality of data strings, and modulates each of the plurality of data strings based on a plurality of carrier signals that are orthogonal to each other. For example, Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX), and Wireless Broadband Internet (Wibro) are communication methods that are based on the OFDM method. According to the OFDM method, mobile communications having fast speed are possible and the efficiency of frequency bandwidth utilization is improved.
However, unlike a Global System for Mobile Communication (GSM) method or a Code Division Multiple Access (CDMA) method, according to the OFDM method, a peak-to-average power ratio of a communication system is increased. That is, according to the OFDM method, since a plurality of modulated signals is transmitted simultaneously, a level of a transmitted signal varies greatly. Thus, according to the OFDM method, the efficiency of a power amplifier included in a transmitter is reduced. Various transmitter structures and transmission methods are suggested in order to overcome the above issues, and a carrier bursting transmitter is one of them.
For example, in the carrier bursting transmitter, a signal (hereinafter referred to as an envelope signal) corresponding to envelope information of a transmitted signal is modulated into a signal having a plurality of logic levels. The modulated signal is re-modulated together with a signal corresponding to phase information of the transmitted signal. The re-modulated signal is amplified by a power amplifier. The power amplifier has a nonlinear output characteristic in general. In order to obtain high efficiency, a typical power amplifier processes a signal having high power in a saturation region. Accordingly, the amplification factor of a signal having high power is less than that of a signal having low power.
If an envelope signal is modulated into a signal having two logic levels (for example, logic ‘0’ and logic ‘1’), the linearity of the modulated signal is not degraded greatly. However, if an envelope signal is modulated into a signal having three or more logic levels, since each logic level has different power, the amplification factor of each signal may vary in each signal interval corresponding to different logic levels. Therefore, the linearity of the modulated signal may be degraded. In order to deal with the above issue, various transmitter structures are suggested. However, according to the suggested transmitter structures, a transmitter requires additional circuits and its power consumption is increased and its efficiency performance is deteriorated.